Efficient removal of oily suspended solids (e.g., oil-coated dirt particles) from water is one of the major challenges in water-treatment industry. For example, large-scale methods for treatment of hydrocarbon-containing waste water (e.g., oil-containing water) in a petroleum industry may range from giant containment booms and absorbent skimmers to chemical treatments. Produced water from unconventional gas production are often disposed of by underground injection. Prior to its disposal, the produced water is treated with significant levels of biocide to prevent fouling of the disposal well. Some of these conventional water-treatment techniques have questionable effects on human health and environment.
Filtration methods could provide a more efficient and scalable approach for treatment of hydrocarbon-containing water and to remove oily suspended particles. Microbial removal by microfiltration has potential to be a lower cost option than biocide treatment. However, for microfiltration to be less expensive than biocide treatment, the microfilter must be hydrophilic and not be fouled by oils present in the produced water. Ceramic membranes that are oil-tolerant have been employed for treatment of oil-containing water. However, ceramic membranes have significant disadvantages in terms of their higher weight and production costs. Further, ceramic membranes have significant limitations in application areas where oily suspended solids are to be removed from contaminated water.
Polymeric membranes are suitable candidates for water treatment processes. Polymeric membranes are cheaper in comparison with their ceramic counter parts and are also more compact. The use of polymeric membranes for treating water reduces the operating cost and size of water-treatment plants employing the same. However, one of the major drawbacks of polymeric membranes is membrane fouling. Generally, membrane fouling occurs when impurities in water such as emulsified, free, or dissolved oil are irreversibly deposited on the membrane surface and/or within the internal pores of the membrane. These deposits not only decrease the membrane lifetime but also lead to a dramatic reduction in water flux, subsequently leading to an increased operating costs. Additionally, if a polymeric membrane is not hydrophilic in nature, aqueous dispersions such as oil-containing waste water cannot be readily filtered through these membranes without pre-wetting the membrane with organic solvents such as isopropanol followed by flushing with water to overcome the lack of affinity between the non-hydrophilic material and the polar aqueous dispersion. Such pre-wetting of membranes may be expensive and may also lead to “gas-lock” or “de-wetting”.
In view of the above, there remains a need for development of hydrophilic polymeric membranes that are both oleophobic and oil-tolerant so as to enable their use in treatment of hydrocarbon-contaminated water without being rapidly fouled by hydrocarbons.